Descending bed, continuously regenerating type filter with an adjustable length wash chamber

ABSTRACT

The present invention relates to a liquid filtering apparatus that includes a vessel which contains a bed of particulate or granular filter medium and a filter-medium washer ( 7 ) located above the upper side of the bed. The apparatus includes circulation means ( 8 ) for continuously transferring dirtied filter medium from a lower part of the bed to the filter-medium washer ( 7 ), and for transferring washed filter medium from the filter-medium washer ( 7 ) to an upper part of the bed. The washer ( 7 ) includes a wash chamber ( 19 ) defined between walls ( 17, 18 ) that have at least a vertical extension. Filter medium is moved down through the wash chamber ( 19 ) while washing liquid is moved up through said chamber. The inventive apparatus also includes means for adjusting the extension of the wash chamber ( 19 ) in the flow direction. The invention also relates to a filtering method of a corresponding kind.

[0001] According to a first aspect, the present invention relates to afiltering apparatus of the kind defined in the preamble of claim 1, andaccording to a second aspect relates to a method of the kind defined inthe preamble of claim 14.

[0002] Filtering apparatus Of this kind are used, among other things, inthe purification of scrubber water, industrial sewage, drinking waterand also in the purification of chemicals, wherewith liquid-carriedcontaminants and solids are filtered out as the liquid passed through abed of filter particles, said filter particles normally being sandalthough not necessarily so. The filter medium may, for instance, beactivated carbon. As the liquid passes through the sand in the filteringprocess, particles carried by the liquid will adhere to and contaminateor dirty the sand particles. It is therefore necessary to reconditionthe contaminated sand, such reconditioning conventionally being effectedin a filter-medium washer located adjacent the actual filtering plant.

[0003] Filtering apparatus of this kind which include a filter-mediumwasher are known, for instance, from SE 7602999-0, SE 7613367-7 and SE8801959-1.

[0004] With filtering apparatus of this kind, the liquid to be filteredis pressed up through a bed of sand hold in a container and the filtrateleaves the container through an outlet located above the bed. The sandis dirtied by the liquid-carried contaminants most heavily at the bottomof the bed. Cleaning of the sand is carried out continuously, by passingsand from the lower part of the bed and up to the filter-medium washer,where the sand passes down through a wash chamber with the aid ofgravity. At the same time, washing liquid is pressed up through the washchamber and washes the sand. The sand falls from the wash chamber andpasses to the upper part of the filter bed. Part of the filtrate is usedas washing liquid and the resultant dirty washing liquid is thendischarged as reject water.

[0005] In the case of SE 7602999-0, for instance, the filter-medium washis located within the container that encloses the sand bed. Dirty sandis shifted to the upper part of the wash chamber with the aid of anairlift pumps while washed sand falls from the lower part of the washchamber down onto the upper side of the bed.

[0006] In order for filtering apparatus of this kind to functionoptimally, the design of the filter-medium washer must be well tunedwith respect to other apparatus components and to the prevailingoperating situation. This can be difficult to achieve at times. On theone hand, the filter-medium washer will preferably have the smallestpossible vertical extension, so as to avoid unnecessarily high plant. Onthe other hand, the washer shall be sufficiently large to ensure thatthe sand will be washed satisfactorily. The throughflow of washingliquid is also a critical parameter. An optimum in this respectconstitutes a compromise between the requirement of a large flow so asto obtain the best possible washing effect, and the desire to restrictthe flow so as not to unnecessarily waste washing liquid. Since thewashing liquid is normally taken from the filtrate generated in thefiltering process, it is desirable that the least possible amount islost in the form of reject liquid.

[0007] Known apparatus of this kind are inflexible with respect toachieving effective washing of the soiled filter medium under theaforesaid conditions. In many cases, this results in plant that cannotoperate optimally and which, in the worst case, can only be made tofunction satisfactorily with difficulty.

[0008] The object of the present invention is to solve this problem andto provide filtering apparatus and a filtering method which enable thefilter-medium washer to be adapted optimally with respect to other plantcomponents and also with respect to the operating situation in question.

[0009] According to a first aspect of the invention, this object isachieved with an apparatus of the kind defined in the preamble of claim1 and having the significant features set forth in the characterisingclause of said claim.

[0010] As a result of the regulating devices with which the apparatus isprovided, the washing process can be optimised with respect to thevertical extension of the wash chamber such that said chamber will havean extension that ensures that the filter medium will be washed to theextent required without needing to over-dimension said chamber and makethe apparatus large and bulky.

[0011] One simple and purposeful method of regulating the verticalextension of the wash chamber is to construct said chamber from a numberof modules that can be connected sealingly to one another anddisconnected from each other such as to enable said vertical extensionto be varied either by adding or removing an appropriate number ofmodules, this being done, for instance, during the trimming phase of theapparatus. Consequently, an apparatus of this design constitutes apreferred embodiment of the invention.

[0012] In the case of a further preferred embodiment of the invention,the washing-liquid outlet means includes a vertically movable spillway.Adjustment of the position of the spillway influences thecounterpressure against which the liquid acts as it flows through thewash chamber, and therewith also influences the rate of flow of saidliquid.

[0013] The filter-medium washer will also preferably be arranged withinthe vessel included in the filtering apparatus, so as to obtain acompact plant, and so that the flows of filtering medium and liquidthrough the apparatus can be favourably formulated.

[0014] The filter-medium washer will conveniently include fully verticalwalls, so that the force of gravity can be utilised in the best way inthe process and stagnation of the filter medium in the wash chamberavoided.

[0015] A suitably designed wash chamber will include two cylindricalwalls that form a ring-shaped wash chamber into which flanges extendfrom said wells. According to one preferred embodiment, each module iscomprised of a wall-part that includes at least one flange.

[0016] In another preferred embodiment of the inventive apparatus, thewashing liquid is comprised of filtrate arriving from the bed andcollected in a container located above the bed. Filtrate is taken fromthe filtrate container through a clean liquid outlet. The pressuregenerated in the container is used to press filtrate through the washchamber, where it is used as washing liquid. According to one preferredembodiment of the invention, the vertical position of the clean-liquidoutlet can be adjusted, so as to adjust the pressure in said containerand therewith the flow of washing liquid through the wash chamber.

[0017] The aforesaid embodiments of the inventive filtering apparatusand other preferred embodiments of said apparatus are set forth in theclaims appended to claim 1.

[0018] According to a second aspect of the invention, the object of theinvention has been achieved by means of a method of the kind defined inthe preamble of claim 14 and comprising the method steps set forth inthe characterising clause of said claim.

[0019] The inventive method affords advantages similar to thosedescribed above with reference to the inventive filtering apparatus.Advantageous embodiments of the inventive method are set forth in theclaims dependent on claim 14.

[0020] The invention will now be described in more detail with referenceto preferred exemplifying embodiments thereof and also with reference tothe accompanying drawings.

[0021]FIG. 1 is a schematic, longitudinal sectional view of a filteringapparatus according to one preferred embodiment of the invention.

[0022]FIG. 2 is a schematic, longitudinal sectional view of part of theapparatus shown in FIG. 1.

[0023]FIG. 3 is a schematic, longitudinal sectional view of part of theapparatus shown in FIG. 1 in accordance with a preferred, alternativeembodiment.

[0024]FIGS. 4 and 5 are sectional views of alternative embodiments of apart shown in FIG. 2.

[0025]FIG. 6 is a schematic, longitudinal sectional view of part of theapparatus shown in FIG. 1.

[0026]FIG. 7 illustrates a first alternative embodiment of a part shownin FIG. 6.

[0027]FIG. 8 illustrates a second alternative embodiment of a part shownin FIG. 6.

[0028]FIG. 1 is a schematic, vertically sectioned view of an inventivefiltering apparatus, and shows how the apparatus is constructed and itsmodus operandi.

[0029] The filtering apparatus comprises a cylindrical vessel 1 having avertically orientated axis. The vessel 1 contains a bed 2 of aparticulate or granular filtering medium, preferably sand. Locatedadjacent the bottom part of the sand bed is an inlet 3 for liquid to befiltered, this liquid normally being dirty water. The water flows upthrough the filter bed in the direction of the arrows A and is filteredas it passes through the bed. Filtered liquid, or filtrate, is collectedin a container 4 which forms the part of the vessel 1 that is locatedabove the bed. The filtered liquid exits from the container 4 through anoutlet conduit 5 connected with the container 4 via a clean-water outlet6 in the form of a spillway. The vertical position of the outlet 6 isdetermined by the upper edge of a wall 33. Although the wall is shown tobe fixed in FIG. 1, it may alternatively be movable vertically so as toenable the level of the outlet 6 to be varied and therewith also thelevel of filtered liquid in the liquid container 4.

[0030] The container 4 accommodates within the vessel 1 a filter-mediumwasher 7 above the sand bed 2. Sand that has been dirtied during thefiltering process is washed in the washer 7. Part of the filtrate isused to wash the sand.

[0031] The filter-medium washer is constructed so that dirty sand willmove down therethrough and meet upwardly flowing liquid filtrate. Sandis delivered with the aid of an airlift pump 8 that extends in aprotective tube 25 along the centre axis of the vessel. Other suitabletypes to pumps may, of course, be used instead. Provided at the bottomof the airlift pulp is a suction opening 9 through which sand is suckedfrom the bottom part of the bed 2, where the sand is dirtiest. The sandis transported up through the airlift pump 9, which extends centrallythrough the filter-medium washer 7 and has an outlet opening 19 whichdischarges above the washer 7, said sand falling gravitationally downinto said outlet. The filter-medium washer also includes a sand outlet11 through which washed sand falls down onto the bed 2, for reuse. Sandis circulated continuously in parallel with the filtering process. Thesand in the sand bed will thus constantly move slowly downwards in thebed as dirty sand is removed from the bottom of the bed, therewithreplenishing the bed with washed sand at the top of the bed. The airliftpump 8 is operated with compressed air delivered through a compressedair conduit 26 that includes a regulating valve 27. The compressed airconduit extends down through the protective tube 25 to the inlet 9 ofthe airlift pump 8 located at the bottom of the bed. Clean water isdelivered to the pump inlet 9 through a clean water conduit 28 whichincludes a regulating valve 29. A splash guard 30 is provided above thefilter-medium washer. A measuring and air-purging pipe 31 that includesa sensor 32 is arranged externally of the container and connected to adecanting valve 33.

[0032] The washer 7 opens downwardly through the sand outlet 11.Consequently, filtrate present in the container 4 will be pressed inthrough the sand outlet 11 by the pressure exerted by the liquid column,up to the level of the spillway 6. The sand outlet 11 thus alsoconstitutes an inlet for filtrate used to wash the sand. The liquidfiltrate used to wash the sand flows out at the upper end of the washer,said upper end being isolated from the container 4 by walls 12, and isdischarged through a reject water conduit 13. The reject water conduitis located beneath the level of the spillway 6, such that the hydraulicpressure will be sufficient to press the reject water out through theconduit 13. The reject water is taken from the reject water conduit to areject water outlet 16, through the medium of a hose 14 and anadjustable spillway 15.

[0033] Thus, the major part of the water entering through the inlet 3and filtered in the bed will leave the apparatus through the outlet 5 asclean water, whereas a minor part of the water used to wash dirty sandwill leave the apparatus through the reject water outlet 16 as dirtyreject water.

[0034]FIG. 2 is an enlarged schematic, longitudinal sectioned view ofthe filter-medium washer 7 shown in FIG. 1.

[0035] The filter-medium washer comprises an inner, tubular wall 17 andan outer tubular wall 18 which is coaxial with the inner wall, saidwalls defining therebetween an annular wash chamber 19. The innertubular wall 17 has disposed therearound a number of flanges 20 whichproject into the wash chamber 19, while flanges 21 project into saidwash chamber from the outer wall 18 in a corresponding manner. Seenaxially, the flanges 21 on the outer wall are located approximatelybetween two adjacent flanges 20 on the inner wall. The flanges (20, 21)on respective inner and outer walls extend roughly halfway into the washchamber. The flanges therewith form an axially extending labyrinthpassageway through which the media flow in zigzag paths, as indicated bythe arrows drawn in the wash chamber. As before mentioned, filteredliquid is pressed in through the opening 11 down to the filter-mediumwasher 7 and pressed up through said chamber. The sand to be washed issucked through the pipe 8 of the airlift pump together with non-filteredwater up to the pump outlet 10, from which the sand runs down into thewash chamber, as indicated by arrows B, through said chamber, and thenfalls out through the opening 11 and down onto the sand bed. As the sandmoves down through the wash chamber 19 through the zigzag path definedby flanges 20, 21, it meets filtered water passing upwardly in acorresponding path, wherewith the sand is washed successively by thewater.

[0036] The cleanliness of the sand thus improves as the sand moves downthrough the wash chamber 19, and the sand that leaves said chamberthrough the opening 11 is, in principle, clean and can be returned tothe bed for reuse. The water flowing up through the wash chamber 19becomes gradually more dirty in a corresponding way, and leaves theapparatus through the reject-water outlet as described above withreference to FIG. 1.

[0037] As will be seen from the Figure, both the outer and the innertubular walls are comprised of a number of respective modules 18 a, 18b, 18 c, etc., and 71 a, 17 b, 17 c, etc. Each module can be detachablyfastened readily to an adjacent module. This ran be achieved, forinstance, by providing one end of a module with a circular groove 22 forpress-fit co-action with the other end of an adjacent module. Othermeans and methods of mutually connecting the modules in a manner whichenables them to be readily disconnected are, of course, conceivable.Each inner-wall module and each outer-wall module of the illustratedembodiment includes only one flange.

[0038] It is also conceivable for each module to include severalflanges, while not all modules need have mutually the same axial lengthand the same number of flanges. For instance, the filter-medium washermay comprise a relatively long basic module which includes a pluralityof flanges and which is connected to a number of shorter, single-flangemodules.

[0039] By varying the number of modules, the length of the washer canthus be adjusted to suit the different degrees of washing requirementson the one hand, and to tune to prevailing pressure conditions on theother hand.

[0040]FIG. 3 illustrates an example of flange construction. The modulesmay comprise ring-shaped elements made of plastic or sheet-metal inwhich each outwardly directed flange 20 has form of a triangularextension in the ring and each inwardly directed flange 21 has the formof a triangular web-part in the ring.

[0041]FIGS. 4 and 5 illustrate respectively an alternative design of theflanges 21, in which said flanges are solid. As evident from theFigures, the flanges may slope on both sides thereof or solely on oneside. The flanges may, of course, have shapes different to those shown,and may also be made of other types of material than those mentioned,without departing from the concept of the invention.

[0042]FIG. 6 is an enlarged, schematic view that illustrates thearrangement of the reject-water outlet. The adjustable spillway 15, towhich the reject-water conduit 13 is connected via the hose 4, can bemoved vertically by means of the rod 23 and locked firmly in a chosenposition by means of a locking knob 24 attached to the rod 23. Thevertical position of the spillway 15 determines the level II of thereject water pressed up from the washer 7. The reference I indicates thelevel of the filtered water in the container 4. The pressure differencerepresented by the level difference between the liquid surfaces I and IIdetermines the force at which the water is pressed up through the washer7, and therewith also the rate of flow of said water. Variation of thevertical position of the spillway 15 will result in correspondingvariation of the distance between I and II, therewith enabling the flowof water through the washer to be regulated. An optimal balance cantherewith be set between the waste of as little water as possible in theform of reject water on the one hand, and requisite washing of the andon the other hand.

[0043]FIG. 7 illustrates an alternative embodiment of the spillway 15,in which a pipe 16 that forms the outlet extends into the spillwayhousing. The pipe can be moved vertically, so as to enable the outletlevel to be varied. Alternatively, the pipe may be fixed and its one endprovided with an axially movable sleeve 34 which determines the outletlevel.

[0044]FIG. 8 illustrates an alternative embodiment of the spillway 15,which includes a partition wall 35 which is axially movable to enablethe outlet level to be adjusted.

[0045] In the case of the embodiments illustrated in FIGS. 7 and 8, theconduit 13 (see FIG. 6) need not be connected to the spillway 15 via ahose 14, which can be replaced with a rigid pipe.

1. A liquid filtering apparatus that includes a vessel (1) whichcontains a bed (2) of particulate or granular filter medium, and afilter-medium washer (7) which is located above the upper side of thebed (2), said apparatus further including circulation means (8) forcontinuously transferring dirty filter medium from a lower part of thebed to said filler-medium washer, and transferring washed filter mediumfrom said washer to an upper part of the bed (2), said washer (7)including a wash chamber (19) defined between walls (17, 18) that haveat least a vertical extension, and said filter medium being moveddownwardly through the wash chamber (19) and washing liquid being movedup through said wash chamber (19), characterised by means for adjustingthe length of the wash chamber (19) in the direction of media flow.
 2. Aliquid filtering apparatus according to claim 1, wherein said adjustmentmeans includes washing-chamber walls (17, 18) which ace each comprisedof a plurality of modules (17 a, 17 b, 17 c; 18 a, 18 b, 18 c) that canbe readily connected together and detached from one another, so as toenable the extension of the wash chamber (19) to be varied by varyingthe number of modules.
 3. A liquid filtering apparatus according toclaim 1 or 2, wherein the filter-medium washer (7) is located withinsaid vessel (1).
 4. A liquid filtering apparatus according to any one ofclaims 1-3, wherein the washer walls (17, 18) extend essentially fullyvertically.
 5. A liquid filtering apparatus according to any one ofclaims 1-4, wherein each wall (17, 18) includes flanges (20, 21) thatproject into the wash chamber and that are vertically offset in relationto one another.
 6. A liquid filtering apparatus according to any one ofclaims 1-5, wherein the walls include an inner cylindrical wall (17)having outwardly extending flanges (20) and an outer cylindrical wall(18) having inwardly extending flanges (21), said walls definingtherebetween an annular wash chamber (19) of circular cross-section. 7.A liquid filtering apparatus according to any one of claims 1-6, whereineach module (17 a, 17 b, 17 c; 18 a, 18 b, 18 c) includes a section ofeach wall having at least one flange.
 8. A liquid filtering apparatusaccording to any one of claims 1-7, wherein the flow regulating means isadapted to regulate the flow of washing liquid through the wash chamber(19).
 9. A liquid filtering apparatus according to claim 8, wherein saidflow regulating means includes outlet conduit means (13, 16) for washingliquid that has passed through the wash chamber (19), said outletconduit means (13, 16) including a vertically movable spillway (15). 10.A liquid filtering apparatus according to any one of claims 1-9, whereinthe washing liquid is comprised of filtrate obtained from the bed (2)and said apparatus further includes a filtrate container (4) whichconstitutes an upward extension of said vessel (1) above the upper sideof the bed (2) and is provided with a clean liquid outlet (6) intendedfor filtrate from the container (4) and located at a level above thehighest point of the wash chamber (19), said filter medium washer (1)having at the bottom thereof a washing liquid inlet (13) whichcommunicates with the container (4) such that filtrate will be pressedup through the wash chamber by static pressure.
 11. A liquid filteringapparatus according to claim 10, wherein said spillway (15) is locatedbeneath said clean liquid outlet (6).
 12. A liquid filtering apparatusaccording to claim 10 or 11, wherein the clean liquid outlet (6) isprovided with means (33) for adjusting its vertical position.
 13. Aliquid filtering apparatus according to any one of claims 1-12, whereinsaid circulation means includes an airlift pump (8) that has afilter-medium inlet (9) at the bottom part of the bed (2), and afilter-medium outlet (12) at a position above the wash chamber (19). 14.A liquid filtering method in which the liquid is caused to pass througha bed of particulate or granular filtering medium and dirty filtermedium is transferred from a lower part of the bed to a filter-mediumwasher and in which washed filter medium is transferred from the washerto an upper part of the bed, wherein said filter medium is caused topass down through a wash chamber defined in the washer by walls whichhave at least a vertical extension, and wherein washing liquid is causedto pass up through said wash chamber, characterised by adjusting theextension of the wash chamber.
 15. A method according to claim 14, inwhich the wash chamber walls are comprised of a plurality of mutuallyconnectable and disconnectable modules, therewith enabling the verticalextension of the wash chamber to be varied by varying the number ofmodules.
 16. A method according to claim 14 or 15, in which the washingliquid is led away from the wash chamber via a spillway, and in whichthe vertical position of the spillway can be adjusted and therewith alsothe flow of washing liquid through the wash chamber.
 17. A methodaccording to any one of claims 14-16, in which the bed is contained in avessel and in which the filtrate is passed from the bed to a liquidcontainer located above sand bed, said container comprising a part ofsaid vessel, and in which the filtrate is used as washing liquid in thefilter-medium washer and pressed therethrough by the static liquidpressure prevailing in said container, said container having a cleanliquid outlet, and in which method the vertical position of the cleanliquid outlet is adjusted such as to adjust the flow of washing liquidthrough the wash chamber.
 18. A method according to any one of claims14-17, as applied with an apparatus according to any one of claims 1-13.